Cathode ray tube deflecting cir



Sept. 14, 1937. A. w. vANcE GATHODE RAY TUBE DEFLECTING CIRCUITS 2Sheets-Sheet 1 Filed March 30,. 1935 INVEN'I'OR HrthurW Vance BMM;

H'T'T'ORNEY Sept. 14, 1937.` A, w, VANCE 2,093,177

CATHODE RAY TUBE DEFLECTING CIRCUITS Filed March 50, 1935 2 Sheets-Sheet2 Plate Gaf/etui rlowr VII/100e,

Patented Sept. 14, 1937 Parar Frlc CATHODE RAY TUBE DEFLECTING CIR-CUITS Arthur W. Vance, Haddoniield, N. J., assigner to Radio Corporationof America, a corporation of Delaware Y Application March 30, 1935,Serial N0. 13,'815

9 Claims.

My invention relates to cathode ray tube deflecting circuits andparticularly to circuits for supplying to deilecting coils a iow ofcurrent having a saw-tooth wave form.

One object of my invention is to provide an improved defiecting circuitlfor producing a ow of current in cathode ray tube deilecting coils whichhas a substantially pure saw-tooth wave form.

m A further object of my invention is to provide a simplified deflectingcircuit which can be synchronized easily and which will supply currenthaving a saw-tooth wave form.

A still further object of my invention is to provide a defiectingcircuit having the minimum number of vacuum tubes for supplying currenthaving a substantially pure saw-tooth wave form.

In one of the preferred embodiments of my invention, two electricdischarge tubes are employed, the output circuit of one tube beingcoupled to the input circuit of the second tube through a wave shapingnetwork. The output circuit of the second tube includes a pair ofdeiiecting coils and the voltage appearing across these coils is fedback to the input circuit of the iirst tube in such phase that thecomplete circuit is self-oscillatory. The first tube is biasedsubstantially to cut-oil, while the second tube is preferably of alarger size which may be biased o for operation along the linear portionof its characteristic.

lOther objects, features and advantages of my invention will appear fromthe following description taken'ln connection with the accompanyingdrawings, in which l Figure 1 is a circuit diagram of a deiiectingcircuit embodying my invention;

Figs. 2 and 3 are circuit diagrams of other embodiments of my invention;

Fig. 4 is a characteristic curve of a tubeshown in Fig. 1; and

Figs. 5 and 6 are curves which are referred to in explaining theoperation of my improved deilecting circuit.

Referring to Fig. `1, the deecting circuit inciudes two electricvdischarge tubes I and 2 which may be oi the three electrode type asillustrated. Preferably, the second tube has 'a considerably greaterpower rating than the first tube, the

50 tube being of the 245 type and the other tube being of the 227 typein the speciiic circuit being described.

The iirst tube has an indirectly heated cathode 3. a control grid 4 anda plate 6. 'I'he plate 6 u is supplied with a suitable positivepotentialy (Cl. Z50-27) through an impedance unit such as a resistor 'Ifrom any suitable source of potential.

The inputcircuit of the tube I includes a grid resistor 8 and aself-biasing resistor 9, the selfbiasing resistor being shunted by acondenser 5 II having a suitable capacity value.

The second tube 2 comprises a directly heated cathode I2, a control gridI3 and a plate I4. The cathode I2 is supplied with current from anysuitable source (not shown), the current source and the cathode beingshunted by a. potentiometer I8.

'I'he input circuit of the tube! includes a grid resistor I1 and aself-biasing resistor I8 which is connected to the midpoint of the po-15 tentiometer I6 in accordance with well known practice. Theself-biasing resistor I8 is shunted by a condenser I9 which has acapacity of the proper value to maintain a substantially steady bias onthe control grid I3. 20

The plate I4 of the tube 2 is supplied with a positive potential throughan impedance unit such as a choke coil 2l from a suitable voltage source(not shown). A pair of defiecting coils of a cathode ray tube (notshown) are indicated 25 at 22, these coils being coupled to the outputcircuit of the tube 2 through a blocking condenser 23 and a conductor24.

The output circuit of the rst tube I is coupled to the input circuit ofthe second tube 2 through 30 a wave shaping network 25 which comprises aresistor 26 and a condenser 21 connected in series. This network isconnected across the output circuit of thefirst tube through a couplingcondenser 28. 'I'he input circuit of the second 35 tube is connectedacross the network 25 through variable tap 29 on the resistor 26. v

It will be evident that if a positive voltage impulse is impressed uponthe grid 4 of the iirst tube, a positive voltage impulse will appear in40 the output circuit of the second tube 2. Thereiore, by coupling theoutput circuit of the second tube to the input circuit of the rst tubethe deiiecting circuit is made self-oscillatory. In the preferredembodiment, this coupling is made through a coupling condenser 3i but itshould be understood that this coupling may be made through atransformer if desired.

One of the features of my invention is that the nrst tube I is normallybiased substantially to 5o plate current cut-of! `while the second tube2 is normally biased to operate along substantially the linear portionof its characteristic. The

characteristic oi the rst tube is shown by the curve 82 in Fig. 4, thedotted line 33 indicating 55 the bias point about which the tube works.It will be apparent that if the grid is swung positive, there will be alarge flow of plate current, while if the grid is swung negative, therewill be only a small plate current iiow.

Before explaining the manner in which the deecting circuit oscillates toproduce a ow of saw-tooth current through the deflecting coils 22, itmay be pointed out that if the deflecting coils 22 are substantiallypurely inductive, (which they are in the preferred circuit) when currenthaving a saw-tooth wave form flows through them, the voltage appearingacross the coils will have the rectangular wave form shown by the curve3@ in Fig. 5. If a voltage having this wave form is impressed upon theinput circuit of the rst tube I, a Voltage having the same wave formwill be impressed across the wave shaping network 25. This voltage willproduce a current flow through the resistor 26 and condenser 2l wherebya voltage impulse having a rectangular wave form will appear across theresistor 26 as indicated by the curve 36 in Fig. 6 and a voltage havinga sawtooth wave form will appear across the condenser 2l as indicated bythe curve 3l in Fig. 6. As ex- 'plained in my VCanadian Patent No..346,227, issued November 20, 1934, by moving the tap 28 along theresistor 2'6 to obtain the proper ratio of rectangular voltage tosaw-tooth voltage, current having a substantially pure saw-tooth waveform will iiow through the deecting coils 22. If the plate impedance ofthe tube 2 is low, only a small saw-tooth component is required in thevoltage impressed upon the grid I3 of that tube. However, if the plateimpedance of the tube is high, as in the case of a screen grid tube, thesaw-tooth component which is required may be much greater than theimpulse component.

Referring now to the manner in which the circuit oscillates, if weassume a small change in a decreasing direction of the plate current ofthe second tube 2, this will swing the grid d of the rst tube positivethrough the coupling condenser 3l. This positive voltage, of course, isput on the grid t as a result of the charging current of the couplingcondenser flowing through the grid resistor 8. As a result of thepositive voltage on the control grid 4, there will be an increase in the-plate current of the tube I whereby there will "be a less positive or.a more negative voltage applied to the control grid I3 of the secondtube, thus further decreasing the plate current of that tube. Thisfurther decrease in plate current applies a still more positivepotential to the grid 4 of the first tube through the coupling condenser3l. It will be seen that this is a curnulative action and that it will`continue until either the plate current of the second tube can decreaseno more or until the plate current of the iirst tube can increase nomore, probably the latter in this particular circuit where the secondtube has a much greater power rating .than the first tube.

As the first tube reaches the condition of plate current saturation v(orthe second tube the condition of cut-off), less charging current is fedthrough the coupling condenser 3I and through the grid resistor ilvwhereby less positive voltage is applied to the grid t. This causes thegrid I3 of the second tube to become less negative whereby the platecurrent of the tube 2 begins to increase.

As a result a negative voltage is applied through the coupling condenser3I to the grid d. This causes the grid I3 of the second tube to becomeThis action is also cumulative and continues either until the platecurrent of the first tube can decrease no more or until the platecurrent of the second tube can increase no more, probably the formercondition because of the high bias on the first tube.

From the above description it will be seen that the voltage whichappears across the deflecting coils 22 is impressed upon the grid t ofthe first tube and that, if there were no resistance in the defiectingcoil circuit, the rectangular voltage impulse appearing across thedeilecting coils (as the result of saw-tooth current flowingtherethrough) would have exactly the wave form required for the voltagewhich is to be impressed upon the grid I3 of the second tube. Since thedeflecting coil circuit includes the plate resistance of the second tube2 as well as a certain amount of resistance in the coils, the waveshaping network 25 is essential because otherwise it would be impossibleto give the deflecting coil current a saw-tooth wave shape; and,consequently, the voltage appearing across the deflecting coils 22 wouldnot have the rectangular wave shape shown in Fig. 5. Furthermore, evenif it did have this rectangular wave shape, the voltage impressed uponthegrid I3 of the second tube would not have the proper wave form sincethe vrequired sawtooth component would be missing.

From the above remarks it will be apparent that in order to obtain avoltage across the wave shaping network 25 which consists of arectangular component and a saw-tooth component, a rectangular voltageWave must be impressed on the grid of the rst tube, and that a voltagehaving this wave form can be obtained from the output circuit of thesecond tube only by passing a substantially pure saw-tooth currentthrough the deflecting coils, the wave shape of the deecting coilcurrent, in turn, being dependent upon the Voltage obtained across thewave shaping network. It might appear that with one unit in the circuitdependent upon another unit in this manner it would be impossible toobtain a satisfactory circuit adjustment. Experience has shown, however,that it is not especially difcult to so adjust a circuit of thischaracter that the current flowing through the deflecting coils willhave a perfect saw-tooth wave form. To adjust the circuit, the couplingcondenser 3l is adjusted to a capacity value such that the circuitoscillates at approximately the desired frequency. Then the variable tap29 is moved along the resistor 26 of the wave shaping network until thewave form of the deecting coil current is made as close to a sawtooth aspossible. This causes a slight change in the frequency of oscillationwhich is corrected for by readjusting the coupling condenser 3l. Thechange in the capacity of the coupling condenser also causes a slightchange in the wave form of the deecting coil current. The adjustment ofthe wave shaping network is again changed to produce a still moreperfect saw-tooth current. After several such circuit adjustments, thecurrent passing through the deecting coils has a perfect saw-tooth waveform.

The reason that the positive voltage impulse impressed upon the grid tof the rst tube through the coupling condenser 3l is of much shorterduration than is the negative voltage impulse, may be explained by thefact that the coupling condenser 3I cannot transfer any direct currentenergy. Therefore, the energy in the positive cycle must equal that inthe negative cycle, or expressing in a diierent way, the area of apositive impulse must equal the area of a negative impulse as indicatedin Fig. 5. Since the iirst tube is biased substantially to cut-off, apositive voltage impressed upon the grid causes a much greater change`in voltage in the output circuit of the second tube than does anegative voltage of equal magnitude. For the areas under the positiveand negative cycles to be equal, the time taken by the negative swing`rnust be considerably longer than the time taken by the positive swing.

The difference in the duration of the positive and negative cycles mayalso be `explained if we assume that the positive impulse fed back tothe grid 4 of the first tube causes the coupling condenser 3I to chargeto a voltage more than sumcient to block the tube i at the end of thepositive impulse. The positive impulse lasts for the time required forthe deiiecting coils 22 to discharge their stored energy through thesecond tube 2.

The first tube remains blocked until the charge on the couplingcondenser 8i has had time to leak oil through the grid resistor 8sumciently to raise the grid bias above the cut-oil value. Thisdetermines the comparatively long duration of the negative cycle.

It should be understood that it is diiiicult to determine the exactoperation of a circuit oi this character, and that, for this reason, Ido not wish t? be limited to any particular theory of opera- Theoperation of the circuit as described above l depends upon using acoupling condenser 8| which has sumciently small capacity. However, if acoupling condenser of large capacity is used. a capacity so large as tohave a very small alternating current impedance at the frequenciesinvolved, the same result can be obtained by givingv the condenser ilshunting the self-bias resistor 8 a suillciently small capacity. If thisembodiment of my invention is employed, the circuit is adiusted the sameas previously described except the capacity of the shunting condenser Ilis adjusted iarstead of the capacity of the couplingrcondenser When thecapacity values indicated in Fig. 1 for condensers Ii and 8l areemployed, the frequency of oscillation is determined mainly by thecapacity of the coupling condenser 8| and to a less extent by thecapacity of the condenser I i.

The above-described detlecting circuit was utilizedfor generatingsaw-tooth deiiecting wavesfor the comparatively high frequencyhorizontal deflection in a television receiver. The circuits shown inFigs. 2 and-3 were designed i'o'r providing the comparatively lowfrequency saw-tooth waves required for vertical deection.

Referring to Fig.r2, the deflecting circuit comprises two screen gridtubes 4i and 42 connected as a direct current ampiier. The first tube 4ihas an indirectly heated cathode 48. a control grid 44, a screen grid 46and a plate 41. A positive potential is supplied to the plate 41 througha plate resistor 48 from a voltage divider 48. The screen grid 48 issupplied with a suitable positive potential.

The input circuit of the tube 4I includes a grid resistor 5I and abiasing resistor 82, the-grid end of the vbiasing resistor 52 beingconnected to the negative terminal of the source of biasing voltage (notshown). I

The secondtube 42 includes an indirectly heated cathode |58, a controlgrid 84, a screen grid 88 and a plate 61. The plate 81 is supplied witha positive potential through a choke coil 58 and a resistor 89 from thevoltage divider 49. The

screen grid 58 is supplied with a lower positive potential from a pointon the voltage divider 48.

The control grid 54 is connected through a conductor 6I directly to theplate 41 oi the first tube. The cathode 58 is connected through aresistor 82 A to the cathode 48 of the iirst tube whereby the ilow ofplate current through the resistor 62 maintains the cathode 68 positivewith respect to the control grid 54. The resistor 62 is shunted by asuitable by-pass condenser 68.

A wave shaplngnetwork 64, similar to the one previously described andcomprising a resistor 6E and a condenser 61, is connected across theinput circuit of the second tube 42.

Cathode ray tube deecting coils indicated at 68 are connected across theoutput circuit of the tube 42, the Yupper terminal of the coils beingconnected to the plate 51 through a coupling condenser 68 and the otherterminal of the coils being connected to the cathode 53 through a con-lductor 1 i.

The output circuit oi the second tube 42 is coupled to the input circuitof the rst tube 4i through a coupling condenser 12. this condenserhaving one plate connected to the junction point of the inductance coli58 and th/e resistor 59 and having the other plate connected to thecontrol grid 44.

In the particular circuit illustrated, synchronizing impulses areapplied through a resistor 13 and a condenser 14 to the plate 41 of thenrst tube. A condenser 18 is connected between the plate end of theresistor 18 and ground so that it, in con- Junction with the resistor13, separates vertical synchronizing impulses irom horizontalsynchronizing impulses. In this circuit. as in the circuit shown in Fig.1, theldeilecting circuit may be synchronized by impressing thesynchronizing im- 4 pulses upon either the plate or the grid of theiirst 18, a control grid 8|, a screen grid 82 and a plate 83.

The plate 88 is supplied through a resistor 84 with a positive potentialfrom a suitable voltage source. The input circuit of the tube 11includes a grid resistor 88 and a self-biasing resistor 81, theself-biasing resistor being shunted by a condenser 88 which, as statedin connection with Fig. 1, may have a large capacity value if a smallcoupling or feed-back condenser is employed. but which must have acomparatively small capacity value if the coupling condenser has a langecapacity.

The second tube 18 includes a cathode 88, a control grid 8| and a plate82. The plate 92 of the second tube is supplied through a choke coil 88with a positive voltage from a suitable voltage source. The inputcircuit of the tube 18 includes a grid resistor 84 and a suitablebiasing source such as a biasing battery 88.

The output -circuit oi the first tube 11 is coupled to the input circuitof the tube 18 through a coupling condenser 81. In this embodiment o!the invention, a wave shaping network 85 comprising a resistor 88 andcondenser 89 in series are connected across the output electrodes of theviirst tube 1l. It will be noted that in this circuit the couplingcondenser 91 is located between the wave shaping network 95 and the grid8l of the second tube, instead of between the wave shaping network andthe plate of the iirst tube as in Fig. 1. Either arrangement givessatisfactory operation. Cathode ray tube deiiecting coils indicated atlill are connected through a coupling condenser I 02 and a Aconductor I0 3 across the output electrodes of the second tube 18. If desired, theymay be shunted b'y a resistor ills for the purpose of improving theeiciency of the circuit as described and claimed in my copendingapplication, Serial No. 741,230, filed August 24, 1934, and assigned tothe same assignee as this application. When using the particular circuitillustrated, it was found desirable to shunt the coils lill by a smallby-pass condenser |06 for the purpose of eliminating certain undesirabletransients in the saw-tooth wave passed through the delecting coils.

As in the circuit shown in Fig. l, the output circuit of the second tubei8 is coupled to the input circuit o f the first tube il through acoupling condenser ll, one plate of the coupling condenser beingconnected to the upper terminal of the deilecting coils itl and theother plate of the condenser being connected to the control grid Si ofthe rst tube. In any of the circuits described, satisfactorysynchronization may be obtained by impressing synchronizing impulsesupon either the grids or the plates of either the first tube or thesecond tube.

It will be understood that the synchronizing voltage impulse should beimpressed upon a, tube electrode in phase with, that is, with the samepolarity as, the voltage appearing on said plate due to theself-oscillation of the circuit. The operation of the circuit shown inFig. 3 as an oscillator for producing a iiow of saw-tooth currentthrough the deecting coils is substantially the same as that of thecircuit shown in Fig. 1.

On' the drawings the values of the circuit elements are indicated inohms, megohms, microfarads, henrys, and number of turns.

From the foregoing description it will be seen that many modications maybe made in my invention without departing from the spirit and scopethereof and I desire, therefore, that only such limitations shall beplaced thereon as are necessitated by the prior art and are set forth inthe appended claims.

I claim as my invention:

1. In combination, a cathode ray tube deecting coil having substantialinductance, an electric discharge tube having an input circuit and anoutput circuit, a second electric discharge tube having an input circuitand an output circuit, the output circuit of said second tube beingcoupled to said coil, a Wave shaping network, means for coupling theoutput circuit of said rst tube to the input circuit of said second tubethrough said network, and means for coupling the output circuit of saidsecond tube to the input circuit of said nrst tube in such phase as toproduce oscillations, the wave form of said oscillations beingdetermined in part by the inductance of said deecting coil, said rsttube being biased substantially to plate current cut-off, and saidnetwork being so designed and adjusted as to cause a saw-tooth currentto iiow through said deflecting coil. v

2. The invention according to claim i characterized in that said networkconsists of a resistor and capacitor in series connected across theinput circuit of said second tube.

3. In apparatus of the class described, an electric discharge tubehaving an input circuit and an output circuit, a second electricdischarge tube having an input circuit and having an outq put circuitwhich is substantially purely inductive, a wave shaping network, meansfor coupling the output circuit of said rst tube to the input -circuitof said second tube through said network,

and means for coupling the output circuit of said second tube to theinput circuit of said iirst .tube in such phase as to produceoscillations,

5. In combination, an electric discharge tube having aninput circuit andan output circuit, a second electric discharge tube having an inputcircuit and an output circuit, a cathode ray tube defiecting coil havingsubstantial inductance, said coil being coupled to said second outputcircuit, a wave shaping network, said irst output circuit being coupledto said second input circuit through said network, and means forcoupling said second output circuit to said rst input circuit wherebyoscillations are produced, the wave form oi said oscillations beingdetermined in part by the inductance of said deiiecting coil, saidnetwork being so designed that in response to a rectangular impulsebeing impressed upon said first input circuit there appears across saidnetwork a voltage having a rectangular component and a saw-toothcomponent.

6. 'Ihe invention according to claim 5 characterized in that the outputcircuit of said rst tube includes a plate resistor connected in serieswith a source of plate potential, and further characterized in that saidnetwork consists of a resistor and condenser in series and connected inshunt to said plate resistor and said source.

7. In apparatus of the class described, an electric dischargetube'having an input circuit and an output circuit, a second electricdischarge tube having an input circuit and having an output circuitwhich is substantially purely inductive, a wave shaping network, meansfor coupling the output circuit of said rst tube to the input circuit ofsaid second tube through said network, and means for coupling the outputcircuit of said second tube to the input circuit of said i'lrst tube insuch phase as to produce oscillations, said network including means forproducing a voltage Wave having a saw-tooth component.

8. In apparatus of the class described, an electric discharge tubehaving an input circuit and an output circuit, a second electricdischarge tube having an input circuit and having an output circuitwhich is substantially purely inductive, a wave shaping network, meansfor coupling the output circuit of said rst tube to the input circuitci.' said second tube through said network, and means for coupling theoutput circuit of said second tube to the input circuit of said firsttube in such phase as to produce oscillations, said network includingmeans for producing a voltage wave having a rectangular impulsecomponent.

9. In combination, an electric discharge tube having an input circuitand an output circuit, a second electric discharge tube having an inputcircuit and an output circuit, a cathode ray tube deecting coil havingsubstantial inductance, said coil being coupled to said second outputcircuit,

a wave shaping network, said rst output cirsaid network being sodesigned that in response cuit being coupled to said second input`circuit to a rectangular impulse being impressed upon through saidnetwork, and means for coupling said iirst input circuit there appearsacross said said second output circuit to said rst input cirnetwork avoltage having the proper wave shape cuit whereby oscillations areproduced, the Wave to produce a ow of saw-tooth current through form ofsaid oscillations being determined in said deiiecting coil.

part by the inductance of said defiecting coil, ARTHUR W. VANCE.

